Electrosurgical methods and systems

ABSTRACT

Electrosurgical methods and systems. At least some of the illustrative embodiments are methods including maintaining plasma proximate to an active electrode in a first energy range, and a second energy range. During periods when plasma is proximate to the active electrode, the illustrative method may include controlling flow of fluid drawn into an aperture of an electrosurgical wand, and in some situations increasing fluid flow drawing into the aperture responsive to the active electrode being in operational relationship with tissue, and in other cases decreasing fluid flow drawing into the aperture responsive to the active electrode being in operational relationship with tissue. Further, during periods when plasma is proximate to the active electrode, the illustrative method may include providing output energy at a default energy setpoint, and then providing output energy at a second energy setpoint.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

BACKGROUND

Electrosurgical systems are used by physicians to perform specificfunctions during surgical procedures. Particular electrosurgicalprocedures may remove several different tissue types. For example,procedures involving the knee or shoulder may remove portions ofcartilage, meniscus, and free floating and/or trapped tissue. In somecases, the removal may be a very slight removal, such as tissuesculpting, and in other cases the more aggressive removal of tissue isused. Removing each different tissue type, and/or aggressiveness,represents a different amount of applied energy, and in the related-artinvolves the use of different electrosurgical wands and differentelectrosurgical controllers. In some cases, a surgeon may forgo use ofthe correct wand, applied energy, and/or electrosurgical controller toreduce expenses of the procedure, when better clinical results may havebeen achieved using multiple electrosurgical wands, energies, and/orcontrollers.

Any advance that makes treatment easier for the surgeon, and achievesbetter results, would provide a competitive advantage.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of exemplary embodiments, reference will nowbe made to the accompanying drawings in which:

FIG. 1 shows an electrosurgical system in accordance with at least someembodiments;

FIG. 2 shows an elevation view of an electrosurgical wand in accordancewith at least some embodiments;

FIG. 3 shows a cross-sectional elevation view of an electrosurgical wandin accordance with at least some embodiments;

FIG. 4 shows both an elevation view of screen electrode, and aperspective view of a distal end of an electrosurgical wand comprisingthe screen electrode, in accordance with at least some embodiments;

FIG. 5 shows an electrical block diagram of a controller in accordancewith at least some embodiments;

FIG. 6 shows an example graph relating output RF energy and aspirationflow of various modes, including setpoints within each mode, inaccordance with at least some embodiments;

FIG. 7 shows, in block diagram form, various control algorithms inaccordance with at least some embodiments;

FIG. 8 shows, in block diagram form, filter algorithms in accordancewith at least some embodiments;

FIG. 9 shows, in block diagram form, various control algorithms inaccordance with at least some embodiments;

FIG. 10 shows a method in accordance with at least some embodiments; and

FIG. 11 shows a method in accordance with at least some embodiments.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, companies that design and manufacture electrosurgicalsystems may refer to a component by different names. This document doesnot intend to distinguish between components that differ in name but notfunction.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection or through anindirect connection via other devices and connections.

Reference to a singular item includes the possibility that there areplural of the same items present. More specifically, as used herein andin the appended claims, the singular forms “a,” “an,” “said” and “the”include plural references unless the context clearly dictates otherwise.It is further noted that the claims may be drafted to exclude anyoptional element. As such, this statement serves as antecedent basis foruse of such exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Lastly, it is to be appreciated that unless definedotherwise, all technical and scientific terms used herein have the samemeaning as commonly understood by one of ordinary skill in the art towhich this invention belongs.

“Plasma” shall mean a low temperature gas formed of vapor bubbles or avapor layer that is capable of emitting an ionized discharge.

“Ablation” shall mean removal of tissue based on tissue interaction witha plasma.

“Mode of ablation” shall refer to one or more characteristics of anablation. Lack of ablation (i.e., a lack of plasma) shall not beconsidered a “mode of ablation.” A mode which performs coagulation shallnot be considered a “mode of ablation.”

“Active electrode” shall mean an electrode of an electrosurgical wandwhich produces an electrically-induced tissue-altering effect whenbrought into contact with, or close proximity to, a tissue targeted fortreatment.

“Return electrode” shall mean an electrode of an electrosurgical wandwhich serves to provide a current flow path for electrical charges withrespect to an active electrode, and/or an electrode of an electricalsurgical wand which does not itself produce an electrically-inducedtissue-altering effect on tissue targeted for treatment.

“Electric motor” shall include alternating current (AC) motors, directcurrent (DC) motors, as well as stepper motors.

“Controlling flow of fluid” shall mean controlling a volume flow rate.Control of applied pressure to maintain a set point pressure (e.g.,suction pressure) independent of volume flow rate of liquid caused bythe applied pressure shall not be considered “controlling flow offluid.” However, varying applied pressure to maintain a set point volumeflow rate of liquid shall be considered “controlling flow of fluid”.

“Output energy” and “output RF energy” shall refer to the rate at whichelectrical energy is provided, transferred, or used over time.

“Energy range” shall refer to a lower limit output energy, upper limitoutput energy, and all the intervening output energies between the lowerlimit and the upper limit. A first energy range and a second energyrange may overlap (e.g., the lower limit of the second energy range maybe an intervening energy in the first energy range), but so long as atleast a portion of each energy range is mutually exclusive, the twoenergy ranges shall be considered distinct for purposes of thespecification and claims.

“Energy setpoint” shall refer to a specific output energy that fallswithin an energy range.

A proximity that is in “operational relationship with tissue” shall meana proximity wherein the tissue interacting with a plasma affects theimpedance presented by the plasma and surrounding fluid to electricalcurrent flow through the plasma and surrounding fluid.

A fluid conduit said to be “within” an elongate shaft shall include notonly a separate fluid conduit that physically resides within an internalvolume of the elongate shaft, but also situations where the internalvolume of the elongate shaft is itself the fluid conduit.

Where a range of values is provided, it is understood that everyintervening value, between the upper and lower limit of that range andany other stated or intervening value in that stated range isencompassed within the invention. Also, it is contemplated that anyoptional feature of the inventive variations described may be set forthand claimed independently, or in combination with any one or more of thefeatures described herein.

All existing subject matter mentioned herein (e.g., publications,patents, patent applications and hardware) is incorporated by referenceherein in its entirety except insofar as the subject matter may conflictwith that of the present invention (in which case what is present hereinshall prevail). The referenced items are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such material by virtue of prior invention.

DETAILED DESCRIPTION

Before the various embodiments are described in detail, it is to beunderstood that this invention is not limited to particular variationsset forth herein as various changes or modifications may be made, andequivalents may be substituted, without departing from the spirit andscope of the invention. As will be apparent to those of skill in the artupon reading this disclosure, each of the individual embodimentsdescribed and illustrated herein has discrete components and featureswhich may be readily separated from or combined with the features of anyof the other several embodiments without departing from the scope orspirit of the present invention. In addition, many modifications may bemade to adapt a particular situation, material, composition of matter,process, process act(s) or step(s) to the objective(s), spirit or scopeof the present invention. All such modifications are intended to bewithin the scope of the claims made herein.

The various embodiments are directed to electrosurgical methods andrelated electrosurgical systems. In particular, the various embodimentsare directed to an electrosurgical system having multiple modes ofablation that are configured for treatment of a specific targeted tissuetype or electrosurgical effect desired, and implemented by a singleelectrosurgical wand and a single electrosurgical controller. In exampleembodiments, the multiple modes of ablation are implemented by a singleactive electrode on the electrosurgical wand, and within each modemultiple energy setpoints may be implemented. The specification firstturns to an illustrative system to orient the reader.

FIG. 1 illustrates an electrosurgical system 100 in accordance with atleast some embodiments. In particular, the electrosurgical system 100comprises an electrosurgical wand 102 (hereinafter “wand 102”) coupledto an electrosurgical controller 104 (hereinafter “controller 104”). Thewand 102 comprises an elongate shaft 106 that defines distal end 108.The elongate shaft 106 further defines a handle or proximal end 110,where a physician grips the wand 102 during surgical procedures. Thewand 102 further comprises a flexible multi-conductor cable 112 housingone or more electrical leads (not specifically shown in FIG. 1), and theflexible multi-conductor cable 112 terminates in a wand connector 114.As shown in FIG. 1, the wand 102 couples to the controller 104, such asby a controller connector 120 on an outer surface of the enclosure 122(in the illustrative case of FIG. 1, the front surface).

Though not visible in the view of FIG. 1, in some embodiments the wand102 has one or more internal fluid conduits coupled to externallyaccessible tubular members. As illustrated, the wand 102 has a flexibletubular member 116, used to provide aspiration at the distal end 108 ofthe wand. In accordance with various embodiments, the tubular member 116couples to a peristaltic pump 118, which peristaltic pump 118 isillustratively shown as an integral component with the controller 104(i.e., residing at least partially within the enclosure 122 of thecontroller 104). In other embodiments, an enclosure for the peristalticpump 118 may be separate from the enclosure 122 for the controller 104(as shown by dashed lines in the figure), but in any event theperistaltic pump is operatively coupled to the controller 104.

The peristaltic pump 118 comprises a rotor portion 124 (hereafter just“rotor 124”) as well as a stator portion 126 (hereafter just “stator126”). The flexible tubular member 116 couples within the peristalticpump 118 between the rotor 124 and the stator 126, and movement of therotor 124 against the flexible tubular member 116 causes fluid movementtoward the discharge 128. While the illustrative peristaltic pump 118 isshown with a two-head rotor 124, varying types of peristaltic pumps 118may be used (e.g., a five-head peristaltic pump). In the context of thevarious embodiments, the peristaltic pump 118 creates avolume-controlled aspiration from a surgical field at the distal end 108of the wand 102, with the control based on a speed of the rotor 124, ascommanded by the controller 104.

Still referring to FIG. 1, a display device or interface device 130 isvisible through the enclosure 122 of the controller 104, and in someembodiments a user may select operational modes of the controller 104 byway of the interface device 130 and related buttons 132. For example,using one or more of the buttons 132 the surgeon may select among modesof ablation, such as: a low mode which may be used for removal ofportions of cartilage; a medium mode which may be used for removal ofmeniscus; a high mode for aggressive removal of tissue; and a vacuummode for removal free floating and/or trapped tissue. The various modesof ablation are discussed more thoroughly below.

In some embodiments the electrosurgical system 100 also comprises a footpedal assembly 134. The foot pedal assembly 134 may comprise one or morepedal devices 136 and 138, a flexible multi-conductor cable 140 and apedal connector 142. While only two pedal devices 136 and 138 are shown,one or more pedal devices may be implemented. The enclosure 122 of thecontroller 104 may comprise a corresponding connector 144 that couplesto the pedal connector 142. A physician may use the foot pedal assembly134 to control various aspects of the controller 104, such as the modeof ablation. For example, pedal device 136 may be used for on-offcontrol of the application of radio frequency (RF) output energy to thewand 102, and more specifically for control of output energy in a modeof ablation. Further, pedal device 138 may be used to control and/or setthe mode of ablation of the electrosurgical system. For example,actuation of pedal device 138 may switch between energy levels createdby the controller 104 and aspiration volume created by the peristalticpump 118. In certain embodiments, control of the various operational orperformance aspects of controller 104 may be activated by selectivelydepressing finger buttons located on handle 110 of wand 102 (the fingerbuttons not specifically shown so as not to unduly complicate thefigure).

The electrosurgical system 100 of the various embodiments may have avariety of modes of ablation which employ Coblation® technology. Inparticular, the assignee of the present disclosure is the owner ofCoblation® technology. Coblation® technology involves the application ofa radio frequency (RF) signal between one or more active electrodes andone or more return electrodes of the wand 102 to develop high electricfield intensities in the vicinity of the target tissue. The electricfield intensities may be sufficient to vaporize an electricallyconductive fluid over at least a portion of the one or more activeelectrodes in the region between the one or more active electrodes andthe target tissue. The electrically conductive fluid may be inherentlypresent in the body, such as blood, or in some cases extracelluar orintracellular fluid. In other embodiments, the electrically conductivefluid may be a liquid or gas, such as isotonic saline. In someembodiments, such as surgical procedures involving a knee or shoulder,the electrically conductive fluid is delivered in the vicinity of theactive electrode and/or to the target site by a delivery system separateand apart from the system 100.

When the electrically conductive fluid is heated to the point that theatoms of the fluid vaporize faster than the atoms recondense, a gas isformed. When sufficient energy is applied to the gas, the atoms collidewith each other causing a release of electrons in the process, and anionized gas or plasma is formed (the so-called “fourth state ofmatter”). Stated otherwise, plasmas may be formed by heating a gas andionizing the gas by driving an electric current through the gas, or bydirecting electromagnetic waves into the gas. The methods of plasmaformation give energy to free electrons in the plasma directly,electron-atom collisions liberate more electrons, and the processcascades until the desired degree of ionization is achieved. A morecomplete description of plasma can be found in Plasma Physics, by R. J.Goldston and P. H. Rutherford of the Plasma Physics Laboratory ofPrinceton University (1995), the complete disclosure of which isincorporated herein by reference.

As the density of the plasma becomes sufficiently low (i.e., less thanapproximately 1020 atoms/cm³ for aqueous solutions), the electron meanfree path increases such that subsequently injected electrons causeimpact ionization within the plasma. When the ionic particles in theplasma layer have sufficient energy (e.g., 3.5 electron-Volt (eV) to 5eV), collisions of the ionic particles with molecules that make up thetarget tissue break molecular bonds of the target tissue, dissociatingmolecules into free radicals which then combine into gaseous or liquidspecies. By means of the molecular dissociation (as opposed to thermalevaporation or carbonization), the target tissue is volumetricallyremoved through molecular dissociation of larger organic molecules intosmaller molecules and/or atoms, such as hydrogen, oxygen, oxides ofcarbon, hydrocarbons and nitrogen compounds. The molecular dissociationcompletely removes the tissue structure, as opposed to dehydrating thetissue material by the removal of liquid within the cells of the tissueand extracellular fluids, as occurs in related art electrosurgicaldesiccation and vaporization. A more detailed description of themolecular dissociation can be found in commonly assigned U.S. Pat. No.5,697,882 the complete disclosure of which is incorporated herein byreference.

The energy density produced by electrosurgical system 100 at the distalend 108 of the wand 102 may be varied by adjusting a variety of factors,such as: the number of active electrodes; electrode size and spacing;electrode surface area; asperities and/or sharp edges on the electrodesurfaces; electrode materials; applied voltage; current limiting of oneor more electrodes (e.g., by placing an inductor in series with anelectrode); electrical conductivity of the fluid in contact with theelectrodes; density of the conductive fluid; and other factors.Accordingly, these factors can be manipulated to control the energylevel of the excited electrons. Since different tissue structures havedifferent molecular bonds, the electrosurgical system 100 may beconfigured to produce energy sufficient to break the molecular bonds ofcertain tissue but insufficient to break the molecular bonds of othertissue. For example, fatty tissue (e.g., adipose) has double bonds thatrequire an energy level higher than 4 eV to 5 eV (i.e., on the order ofabout 8 eV) to break. Accordingly, the Coblation® technology in somemodes of operation does not ablate such fatty tissue; however, theCoblation® technology at the lower energy levels may be used toeffectively ablate cells to release the inner fat content in a liquidform. Other modes of operation may have increased energy such that thedouble bonds can also be broken in a similar fashion as the single bonds(e.g., increasing voltage or changing the electrode configuration toincrease the current density at the electrodes). A more completedescription of the various phenomena can be found in commonly assignedU.S. Pat. Nos. 6,355,032; 6,149,120 and 6,296,136, the completedisclosures of which are incorporated herein by reference.

The inventors now present a theoretical underpinning to explain howmultiple modes of ablation may be implemented with a single wand 102 anda single controller 104. However, the theoretical basis is presentedmerely as one possible explanation, and shall not be read as alimitation on the operation of the various embodiments. Anothertheoretical basis may be equivalently proffered, and attempting toexplain operation of a device using a different theoretical basis shallnot obviate whether such a device falls within the appended claims. Inparticular, the electrode circuit, including the plasma created andmaintained in operational relationship to an active electrode of a wand,the fluid between the active and return electrode, and theelectrode-fluid interface, has or presents a certain amount of impedanceto the flow of output energy away from the active electrode toward areturn electrode. The impedance presented by the electrode circuit maybe dependent on many factors, including but not limited to the thicknessand volume of the plasma itself, the surface area of the activeelectrode not covered by a vapor layer and directly in contact with theconductive fluid, and the volume flow of fluid and/or gasses away fromthe location of the plasma.

In related-art devices, only the vacuum pressure used for aspiration iscontrolled (e.g., the vacuum available at wall socket connections in ahospital operating room). However, the vacuum available at a wall socketconnection may be highly variable from room to room, and in many caseswithin the same room over time. Moreover, control of vacuum pressureapplied does not imply a controlled volume of aspiration. Thus, whilerelated-art devices may control vacuum pressure, they do not controlvolume flow rate of the aspiration.

The inventors have found that the relationship of the volume of flow offluid of the aspiration to output energy dissipation is counter to theprevailing understanding. That is, related-art devices and methodsoperate under the assumption that a generally high flow rate morerapidly carries away output energy and thus reduces thermal aspects ofthe ablation. By contrast, the inventors have found that high volumeflow of aspiration tends to cause higher output energy dissipationoverall. With respect to the plasma, the inventors have found thathigher volume flow rates drive both the impedance of the plasma and ofthe electrode circuit down, which increases the output energydissipation. Moreover, higher volume flow rates cause the plasma to“flicker”. Consider an analogy in the form of a candle. If a candle isburning in a room with very little air movement, the flame may be asteady shape, size, and location. However, in the presence of airflow(e.g., a ceiling fan), the flame tends to “flicker”. If one considersthat during periods of time of plasma collapse (i.e., absence of plasma)greater output energy is dissipated in a thermal mode through thesurrounding fluid and tissue, “flickering” plasma caused by high volumeflow rate may result in more output energy dissipation in the tissue andsurrounding fluid, rather than less. That is, not only will the“flickering” plasma present a lower average impedance and thus higheroutput energy dissipation, but also the thermal mode that dominatesduring momentary plasma collapse present in “flicker” causes higheroutput energy dissipation than periods of time when plasma is present.

The finding that the volume flow of fluid of the aspiration isproportional to output energy dissipation is counter to the prevailingunderstanding. That is, related-art devices and methods operate underthe assumption that a generally high flow rate more rapidly carries awayoutput energy and thus reduces thermal aspects of the ablation. Bycontrast, the inventors have found that high volume flow of aspirationtends to cause higher output energy dissipation overall. With respect tothe plasma, the inventors have found that higher volume flow rates drivethe impedance of the plasma down, which increases the output energydissipation. Moreover, higher volume flow rates cause the plasma to“flicker”. Consider an analogy in the form of a candle. If a candle isburning in a room with very little air movement, the flame may be asteady shape, size, and location. However, in the presence of airflow(e.g., a ceiling fan), the flame tends to “flicker”. If one considersthat during periods of time of plasma collapse (i.e., absence of plasma)greater output energy is dissipated in a thermal mode through thesurrounding fluid and tissue, “flickering” plasma caused by high volumeflow rate may result in more output energy dissipation in the tissue andsurrounding fluid, rather than less. That is, not only will the“flickering” plasma present a lower average impedance and thus higheroutput energy dissipation, but also the thermal mode that dominatesduring momentary plasma collapse present in “flicker” causes higheroutput energy dissipation than periods of time when plasma is present.

Accordingly, the embodiments described herein are related to a systemwherein the impedance at the electrode is (directly or indirectly)monitored and used as a parameter to control the volume flow rate ofaspiration in order to control the plasma field in a way that isdesirable for a specific tissue type or procedure. For example, in somemodes of ablation if the impedance at the active electrode is observedto decrease at a point during a procedure (possibly indicating plasmainstability), the system may direct the peristaltic pump to decrease theaspiration flow rate to enable the plasma field to stabilize. Fromanother perspective, it may be desirable to measure the RF electricalcurrent applied to the active electrode and adjust the peristaltic pump(and thus the fluid flow) in order to keep the RF electrical current ata certain predetermined and desired level associated with the mode ofablation. Reference is also made to commonly assigned U.S. Pat. No.8,192,424, titled “ELECTROSURGICAL SYSTEM WITH SUCTION CONTROL APPARTUS,SYSTEM AND METHOD” the complete disclosure of which is incorporatedherein by reference for all purposes. Conversely, it may be desirable incertain modes of ablation to trade off plasma field stability in orderto have higher overall aspiration fluid flow volume in order to removebubbles and debris from the surgical field.

Based on the theoretical underpinning in the paragraphs above, thevarious embodiments are directed to systems and related methodsimplementing at least two modes of ablation during an electrosurgicalprocedure, in some embodiments using a single wand (and in some cases asingle active electrode) along with a single controller. In a particularembodiment, four different modes of ablation may be implemented, suchas: a “low mode” which may be used for the treatment and removal ofportions of sensitive tissue such as portions of articular cartilage; a“medium mode” which may be used for the treatment and removal ofmeniscus; a “high mode” for aggressive removal of tissue of any kind;and a “vacuum mode” for removal free floating and/or trapped tissue.Moreover, some example systems implement multiple energy/flow setpointswithin a single mode of ablation. For example, the “low mode” ofablation may comprise a default setpoint energy/flow, but a surgeon maychoose an increased energy/flow setpoint within the energy rangeassociated with the “low mode” of ablation. Likewise, the surgeon maychoose a decreased energy/flow setpoint in relation to the defaultsetpoint yet still within the energy range associated with the “lowmode” of ablation. More detail regarding the illustrative modes ofablation, and setpoints within each mode, is presented below, after adiscussion of an illustrative wand 102 and internal components of thecontroller 104.

FIG. 2 shows an elevation view of wand 102 in accordance with examplesystems. In particular, wand 102 comprises elongate shaft 106 which maybe flexible or rigid, a handle 110 coupled to the proximal end of theelongate shaft 106, and an electrode support member 200 coupled to thedistal end of elongate shaft 106. Also visible in FIG. 2 is the flexibletubular member 116 extending from the wand 102 and the multi-conductorcable 112. The wand 102 comprises an active electrode 202 disposed onthe distal end 108 of the elongate shaft 106. Active electrode 202 maybe coupled to an active or passive control network within controller 104(FIG. 1) by means of one or more insulated electrical connectors (notshown) in the multi-conductor cable 112. The active electrode 202 iselectrically isolated from a common or return electrode 204 which isdisposed on the shaft proximally of the active electrode 202, in someexample systems within 1 millimeter (mm) to 25 mm of the distal tip.Proximally from the distal tip, the return electrode 204 is concentricwith the elongate shaft 106 of the wand 102. The support member 200 ispositioned distal to the return electrode 204 and may be composed of anelectrically insulating material such as epoxy, plastic, ceramic,silicone, glass or the like. Support member 200 extends from the distalend 108 of elongate shaft 106 (usually about 1 to 20 mm) and providessupport for active electrode 202.

FIG. 3 shows a cross-sectional elevation view of the wand 102 inaccordance with example embodiments. In particular, wand 102 comprises asuction lumen 300 defined within the elongate shaft 106. In the examplewand 102 of FIG. 3, the inside diameter of the elongate shaft 106defines the section lumen 300, but in other cases a separate tubingwithin the elongate shaft 106 may define the suction lumen 300. Thesuction lumen 300 may be used for aspirating excess fluids, bubbles,tissue fragments, and/or products of ablation from the target siteproximate to the active electrode 202. Suction lumen 300 extends intothe handle 110 and fluidly couples to the flexible tubular member 116for coupling to the peristaltic pump 118. Handle 110 also defines aninner cavity 302 within which electrical conductors 210 may reside,where the electrical conductors 210 may extend into the multi-conductorcable 112 and ultimately couple to the controller 104. The electricalconductors likewise extend through the elongate shaft and couple, oneeach, to the return electrode 204 and the active electrode 202, but theelectrical conductors 210 are not shown to reside within the elongateshaft 106 so as not to unduly complicate the figure.

In some systems, the wand 102 may further comprise a temperaturemeasurement device 304 in operational relationship to the flexibletubular member 116. As illustrated in FIG. 3, the temperaturemeasurement device resides within the inner cavity 302 defined by thehandle 110, but the temperature measurement device may be placed at anysuitable location. The temperature measurement device 304 is used todirectly or indirectly measure the temperature of the fluid within thetubular member 116. As illustrated, the temperature measurement device304 abuts an outer surface of the tubular member 116 such that as fluidstravel within the tubular member 116 past the location of thetemperature measurement device 304, localized temperature changes can beread. The temperature measurement device 304 may take any suitable form,such as a resistive thermal device (RTD), a thermistor, an opticaltemperature probe, or a thermocouple. The temperature measurement devicemay be useful in a variety of operational circumstances, such as clogdetection discussed more below.

FIG. 4 shows an elevation view of an example active electrode (on theleft), as well as a perspective view of the distal end of wand 102 (onthe right), in accordance with example systems. In particular, activeelectrode 202 may be an active screen electrode 400 as shown in FIG. 4.Screen electrode 400 may comprise a conductive material, such astungsten, titanium, molybdenum, platinum, or the like. Screen electrode400 may have a diameter in the range of about 0.5 to 8 mm, in some casesabout 1 to 4 mm, and a thickness of about 0.05 to about 2.5 mm, in somecases about 0.1 to 1 mm. Screen electrode 400 may comprise a pluralityof apertures 402 configured to rest over an aperture or distal opening404 of the suction lumen. Apertures 402 are designed to enable thepassage of aspirated excess fluids, bubbles, and gases from the ablationsite and are large enough to enable ablated tissue fragments to passthrough into suction lumen 206 (FIG. 3). As shown, screen electrode 400has an irregular shape which increases the edge to surface-area ratio ofthe screen electrode 400. A large edge to surface-area ratio increasesthe ability of screen electrode 400 to initiate and maintain a plasmalayer in conductive fluid because the edges generate higher currentdensities, which a large surface area electrode tends to dissipate powerinto the conductive media.

In the representative embodiment shown in FIG. 4, screen electrode 400comprises a body 406 that rests over insulative support member 200 andthe distal opening 404 to suction lumen 206. Screen electrode 400further comprises tabs 408, in the example screen electrode 400 of FIG.4, five tabs 408 are shown. The tabs 408 may rest on, be secured to,and/or be embedded in insulative support member 200. In certainembodiments, electrical connectors extend through insulative supportmember 200 and are coupled (i.e., via adhesive, braze, weld, or thelike) to one or more of tabs 408 in order to secure screen electrode 400to the insulative support member 200 and to electrically couple screenelectrode 400 to controller 104 (FIG. 1). In example systems, screenelectrode 400 forms a substantially planar tissue treatment surface forsmooth resection, ablation, and sculpting of the meniscus, cartilage,and other tissues. In reshaping cartilage and meniscus, the physicianoften desires to smooth the irregular and ragged surface of the tissue,leaving behind a substantially smooth surface. For these applications, asubstantially planar screen electrode treatment surface provides thedesired effect. The specification now turns to a more detaileddescription of the controller 104.

FIG. 5 shows an electrical block diagram of controller 104 in accordancewith at least some embodiments. In particular, the controller 104comprises a processor 500. The processor 500 may be a microcontroller,and therefore the microcontroller may be integral with read-only memory(ROM) 502, random access memory (RAM) 504, digital-to-analog converter(D/A) 506, analog-to-digital converter (A/D) 514, digital outputs (D/O)508, and digital inputs (D/I) 510. The processor 500 may further provideone or more externally available peripheral busses, such as a serial bus(e.g., I²C), parallel bus, or other bus and corresponding communicationmode. The processor 500 may further be integral with communication logic512 to enable the processor 500 to communicate with external devices, aswell as internal devices, such as display device 130. Although in someembodiments the processor 500 may be implemented in the form of amicrocontroller, in other embodiments the processor 500 may beimplemented as a standalone central processing unit in combination withindividual RAM, ROM, communication, A/D, D/A, D/O, and D/I devices, aswell as communication hardware for communication to peripheralcomponents.

ROM 502 stores instructions executable by the processor 500. Inparticular, the ROM 502 may comprise a software program that, whenexecuted, causes the controller to implement two or more modes ofablation, including increasing and decrease peristaltic pump speedresponsive to various feedback parameters (discussed more below). TheRAM 504 may be the working memory for the processor 500, where data maybe temporarily stored and from which instructions may be executed.Processor 500 couples to other devices within the controller 104 by wayof the digital-to-analog converter 506 (e.g., in some embodiment the RFvoltage generator 516), digital outputs 508 (e.g., in some embodimentthe RF voltage generator 516), digital inputs 510 (e.g., interfacedevices such as push button switches 132 or foot pedal assembly 134(FIG. 1)), and communication device 512 (e.g., display device 130).

Voltage generator 516 generates an alternating current (AC) voltagesignal that is coupled to active electrode 202 of the wand 102 (FIG. 3).In some embodiments, the voltage generator defines an active terminal518 which couples to electrical pin 520 in the controller connector 120,electrical pin 522 in the wand connector 114, and ultimately to theactive electrode 202 (FIG. 3). Likewise, the voltage generator defines areturn terminal 524 which couples to electrical pin 526 in thecontroller connector 120, electrical pin 528 in the wand connector 114,and ultimately to the return electrode 204 (also see FIG. 3). Additionalactive terminals and/or return terminals may be used. The activeterminal 518 is the terminal upon which the voltages and electricalcurrents are induced by the voltage generator 516, and the returnterminal 524 provides a return path for electrical currents. It would bepossible for the return terminal 524 to provide a common or ground beingthe same as the common or ground within the balance of the controller104 (e.g., the common 530 used on push-buttons 132), but in otherembodiments the voltage generator 516 may be electrically “floated” fromthe balance of the controller 104, and thus the return terminal 524,when measured with respect to the common or earth ground (e.g., common530) may show a voltage; however, an electrically floated voltagegenerator 516 and thus the potential for voltage readings on the returnterminals 524 relative to earth ground does not negate the returnterminal status of the terminal 524 relative to the active terminal 518.

The AC voltage signal generated and applied between the active terminal518 and return terminal 524 by the voltage generator 516 is RF energythat, in some embodiments, has a frequency of between about 5 kilo-Hertz(kHz) and 20 Mega-Hertz (MHz), in some cases being between about 30 kHzand 2.5 MHz, in other cases being between about 50 kHz and 500 kHz,often less than 350 kHz, and often between about 100 kHz and 200 kHz. Insome applications, a frequency of about 100 kHz is useful because targettissue impedance is greater at 100 kHz.

The RMS (root mean square) voltage generated by the voltage generator516 may be in the range from about 5 Volts (V) to 1800 V, in some casesin the range from about 10 V to 500 V, often between about 10 V to 400 Vdepending on the mode of ablation and active electrode size. Thepeak-to-peak voltage generated by the voltage generator 516 for ablationin some embodiments is a square waveform with a peak-to-peak voltage inthe range of 10 V to 2000 V, in some cases in the range of 100 V to 1800V, in other cases in the range of about 28 V to 1200 V, and often in therange of about 100 V to 320V peak-to-peak.

The voltage and current generated by the voltage generator 516 may bedelivered in a series of voltage pulses or AC voltage with asufficiently high frequency (e.g., on the order of 5 kHz to 20 MHz) suchthat the voltage is effectively applied continuously (as compared with,e.g., lasers claiming small depths of necrosis, which are pulsed about10 Hz to 20 Hz). In addition, the duty cycle (i.e., cumulative time inany one-second interval that energy is applied) of a square wave voltageproduced by the voltage generator 516 is on the order of about 50% forsome embodiments as compared with pulsed lasers which may have a dutycycle of about 0.0001%. Although square waves are generated and providedin some embodiments, the AC voltage signal is modifiable to include suchfeatures as voltage spikes in the leading or trailing edges of eachhalf-cycle, or the AC voltage signal is modifiable to take particularshapes (e.g., sinusoidal, triangular).

The voltage generator 516 delivers average power levels ranging fromseveral milliwatts to hundreds of watts per electrode, depending on themode of ablation and state of the plasma proximate to the activeelectrode. The voltage generator 516 in combination with the processor500 are configured to initially set the output energy of the voltagegenerator 516 (e.g., by controlling output voltage) based on the mode ofablation selected by the surgeon, and in some cases the setpoint withinthe particular mode of ablation. Moreover, while in a selected mode ofablation and setpoint within the mode of ablation, the processor 500and/or voltage generator 516 may make control changes to compensate forchanges caused by use of the wand. The control changes are discussedmore below after a further discussion of the peristaltic pump 118. Adescription of various voltage generators 516 can be found in commonlyassigned U.S. Pat. Nos. 6,142,992 and 6,235,020, the complete disclosureof both patents are incorporated herein by reference for all purposes.Reference is also made to commonly assigned U.S. Pat. No. 8,257,350,entitled “METHOD AND SYSTEM OF AN ELECTROSURGICAL CONTROLLER WITHWAVE-SHAPING”, the complete disclosure of which is incorporated hereinby reference as if reproduced in full below.

In some embodiments, the various modes of ablation implemented by thevoltage generator 516 (along with the peristaltic pump 118) may becontrolled by the processor 500 by way of digital-to-analog converter506. For example, the processor 500 may control the output voltages byproviding one or more variable voltages to the voltage generator 516,where the voltages provided by the digital-to-analog converter 506 areproportional to the voltages to be generated by the voltage generator516. In other embodiments, the processor 500 may communicate with thevoltage generator by way of one or more digital output signals from thedigital output converter 508, or by way of packet-based communicationsusing the communication device 512 (the communication-based embodimentsnot specifically shown so as not to unduly complicate FIG. 5).

Still referring to FIG. 5, in some embodiment the controller 104 furthercomprises a mechanism to sense the electrical current provided to theactive electrode. In the illustrative case of FIG. 3, sensing currentprovided to the active electrode may be by way of a current sensetransformer 532. In particular, current sense transformer 532 may have aconductor of the active terminal 518 threaded through the transformersuch that the active terminal 518 becomes a single turn primary. Currentflow in the single turn primary induces corresponding voltages and/orcurrents in the secondary. Thus, the illustrative current sensetransformer 532 is coupled to the analog-to-digital converter 514 (asshown by the bubble A). In some cases, the current sense transformer maycouple directly to the analog-to-digital converter 514, and in othercases additional circuitry may be imposed between the current sensetransformer 532 and the analog-to-digital converter 514, such asamplification circuits and protection circuits. For example, in oneexample system the current sense transformer 532 is coupled to anintegrated circuit device that takes the indication of current from thecurrent sense transformer 532, calculates a root-mean-square (RMS)current value, and provides the RMS current values to the processor 500through any suitable communication system (e.g., as an analog valueapplied the A/D 514, as a digital value applied to the multiple inputsof the D/I 510, as a packet message through the communication port 512).The current sense transformer is merely illustrative of any suitablemechanism to sense the current supplied to the active electrode, andother systems are possible. For example, a small resistor (e.g., 1 Ohm,0.1 Ohm) may be placed in series with the active terminal 518, and thevoltage drop induced across the resistor used as an indication of theelectrical current.

Given that the voltage generator 516 is electrically floated, themechanism to sense current is not limited to the just the activeterminal 518. Thus, in yet still further embodiments, the mechanism tosense current may be implemented with respect to the return terminal524. For example, illustrative current sense transformer 532 may beimplemented on a conductor associated with the return terminal 524.

In some example systems, the feedback parameter used by the processor500 regarding the voltage generator 516 is the electrical current flow.For example, in systems where the voltage generator can accuratelyproduce an output voltage independent of the impedance of the attachedload, the processor 500 having set point control for the voltage createdby the voltage generator 516 may be sufficient (e.g., to calculate avalue indicative of impedance of the electrode circuit and plasmaproximate the active electrode). However, in other cases, voltage toomay be a feedback parameter. Thus, in some cases the active terminal 518may be electrically coupled to the analog-to-digital converter 514 (asshown by bubble B). However, additional circuitry may be imposed betweenthe active terminal 518 and the analog-to-digital converter 514, forexample various step-down transformers, protection circuits, andcircuits to account for the electrically floated nature of the voltagegenerator 516. Such additional circuitry is not shown so as not tounduly complicate the figure. In yet still other cases, voltage sensecircuitry may measure the voltage, and the measured voltage values maybe provided other than by analog signal, such as by way of packet-basedcommunications over the communication port 512 (not shown so as not tounduly complicate the drawing).

Still referring to FIG. 5 (and also FIG. 1), controller 104 inaccordance with various embodiments further comprises the peristalticpump 118. The peristaltic pump 118 may reside at least partially withinthe enclosure 122. The peristaltic pump comprises the rotor 124mechanically coupled to a shaft of the electric motor 534. In somecases, and as illustrated, the rotor of the electric motor may coupledirectly to the rotor 124, but in other cases various gears, pulleys,and/or belts may reside between the electric motor 534 and the rotor124. The electric motor 534 may take any suitable form, such as an ACmotor, a DC motor, and/or a stepper-motor. To control speed of the shaftof the electric motor 534, and thus to control speed of the rotor 124(and the volume flow rate at the wand), the electric motor 534 may becoupled to a motor speed control circuit 536. In the illustrative caseof an AC motor, the motor speed control circuit 536 may control thevoltage and frequency applied to the electric motor 534. In the case ofa DC motor, the motor speed control circuit 536 may control the DCvoltage applied to the electric motor 534. In the case of astepper-motor, the motor speed control circuit 536 may control thecurrent flowing to the poles of the motor, but the stepper-motor mayhave a sufficient number of poles, or is controlled in such a way, thatthe rotor 124 moves smoothly. Stated otherwise, the rotor 124 movessmoothly due to the high number of steps per turn.

The processor 500 couples to the motor speed control circuit 536, suchas by way of the digital-to-analog converter 506 (as shown by bubble C).The processor 500 may be coupled in other ways as well, such aspacket-based communication over the communication port 512. Thus, theprocessor 500, running a program, may read electrical current suppliedon the active terminal 518, may read voltage supplied on the activeterminal 518, and responsive thereto may make speed control changes (andthus volume flow rate changes) by sending speed commands to the motorspeed control circuit 536. The motor speed control circuit 536, in turn,implements the speed control changes. Speed control changes may comprisechanges in speed of the rotor 124 when desired, stopping the rotor 124when desired, and in some modes of ablation temporarily reversing therotor 124.

The specification now turns to a more detailed description of thevarious modes of ablation that may be implemented by the electrosurgicalsystem. Each mode of ablation is illustratively named based on theaggressiveness of the ablation. However, all the illustrativelyidentified tissue types may be ablated in each and every mode, and thusproviding an indication of the type of tissue expected to be ablated ineach mode shall not be read as a limitation of the applicability of anyparticular mode. Ablating tissue in a mode not specifically designed forthe tissue may result in unwanted effects, such as discoloration orremoval of too much of the target tissue or removal at a rate deemed toorapid. The available modes of ablation of the system thereby provideenhanced performance where the management of output energy inconjunction with control of aspiration flow rates creates surgicalresults in each mode that are tuned to the targeted tissue, the rate ofaggressiveness, or type of surgical procedure.

In accordance with the various embodiments, the electrosurgicalcontroller 100 implements at least two, and in some embodiments four,modes of ablation to modulate the flow rate dynamically in the vicinityof an active electrode in order to regulate the RF output energy: a “lowmode” which may be used for treatment, ablation, and removal of portionsof cartilage; a “medium mode” which may be used for treatment, ablation,and removal of meniscus; a “high mode” which may be used for aggressivetreatment, ablation, and removal of tissue; and a “vacuum mode” forremoval of loose, free floating and/or trapped tissue. Each illustrativemode of ablation may be characterized by a range of energies that may beapplied to the active electrode (hereafter just “energy range”) and acorresponding range of aspiration flows. During operation within aparticular mode of ablation, the output energy provided by the voltagegenerator 516 and volume flow rate provided by the peristaltic pump 118(FIG. 1) may change based on operational conditions at the distal end108 of the wand, but such changes shall not obviate the status of beingwithin a particular mode of ablation. The following table characterizesat a high level the four illustrative modes of ablation.

TABLE 1 Low Mode Medium Mode High Mode Vacuum Mode Low output energyMedium output energy High output energy Low to High output energy toactive electrode. to active electrode. to active electrode. to activeelectrode. Low aspiration Medium aspiration High aspiration Very high orpulsed flow. flow. flow. aspiration flow.Each mode will be discussed in turn.

The low mode is designed specifically for the treatment and selectiveablation of articular cartilage or other very sensitive tissue. This lowmode is particularly appropriate for chondroplasty and meniscusfinishing or sculpting. However, cartilage does not re-grow, and thusthe amount of cartilage ablated by a surgeon during a chondroplastyprocedure is in most procedures very small. The primary concern of thesurgeon may be to carefully remove diseased cartilage while at the sametime reducing the damage to the underlying chondral tissue that remains.For these reasons, the illustrative low mode is characterized by lowoutput energy provided to the active electrode, as well as low volumeflow rate for the aspiration. In particular, in this mode of ablationoutput energy delivery during treatment is desired to increase cellviability and to create reduced instantaneous output energy dissipationand heat production in the vicinity of the treatment site. The reducedsuction flow and low volume flow rate associated with this mode ofoperation may result in a plasma and electrode circuit having a higheroverall impedance.

In the low mode of ablation, the processor 500, executing a program,controls the voltage generator 516 and peristaltic pump 118 to implementrelatively high target impedance for the electrode circuit, and to avoidplasma collapse. In some embodiments, the controller 104 may providepredetermined output energy, and for impedance values falling within apredetermined range, the controller 104 may control impedance basedsolely on changes in speed of the peristaltic pump 118. For variationsin impedance that fall outside with a predetermined range, the controlstrategy may also rely on changes in output energy supplied by thevoltage generator 516. For example, control action in response todecreasing impedance (as calculated based on the current and/or voltageapplied to the active electrode) may involve slowing, stopping, ortemporarily reversing the peristaltic pump 118 (FIG. 1), and in somesystems increasing the output energy supplied by the voltage generator516. In some embodiments, changes in the electrical output energyproduced by the voltage generator 516 may be implemented more quicklythan changes in peristaltic pump 118 speed, and thus in some embodimentsan initial reaction to measured decreasing electrode circuit impedancemay be momentarily increasing the level of supplied output energy,followed by decreasing pump speed and lowering again the supplied outputenergy.

The medium mode of operation is designed specifically for ablation offibro-cartilaginous tissue like meniscal tissue, but other types oftissue may also be ablated in the medium mode. This medium mode may alsobe appropriate for the electrosurgical treatment of labrum tissue. Whenablating meniscus, the surgeon may be interested in ablating more tissuevolume than with respect to cartilage, but browning of the remainingmeniscus is disfavored. For at least this reason, the illustrativemedium mode is characterized by medium output energy provided to theactive electrode, as well as medium volume flow rate of the aspirationin order to preserve tissue consistency. In particular, in this mode ofablation output energy delivery during treatment is desired to increasetissue matrix preservation and to reduce tissue matrix alteration withreduced or no tissue discoloration, or cross-linking of the collagenfibers that could result in mechanical alterations. The medium volumeflow rate may result in the electrode circuit having a lower impedancethan the low mode.

In the medium mode of ablation, the processor 500, executing a program,controls the voltage generator 516 and peristaltic pump 118 (FIG. 1) toimplement a medium target impedance for the electrode circuit. In someembodiments, the controller 104 may provide predetermined output energy,and for impedance values falling within a predetermined range, thecontroller 104 may control impedance based by changing speed of theperistaltic pump 118. For variations in impedance that fall outside of apredetermined range, the control strategy may also rely on changes inoutput energy supplied by the voltage generator 516. For example,control action in response to decreasing impedance (as calculated basedon the current and/or voltage applied to the active electrode) mayinvolve slowing and/or stopping the peristaltic pump 118, and in somesystems increasing the output energy supplied by the voltage generator516. In some embodiments, changes in the electrical output energyproduced by the voltage generator 516 may be implemented more quicklythan changes in peristaltic pump 118 speed, and thus in some embodimentsan initial reaction to measured decreasing electrode circuit impedancemay be momentarily increasing the level of supplied output energy,followed by decreasing pump speed and lowering again the supplied outputenergy.

The illustrative high mode of ablation is designed specifically forquickly removing tissue. By way of example, the high mode may be usedfor sub-acromial decompression treatments or ACL stump debridement. Forthis reason, the illustrative high mode is characterized by high outputenergy provided to the active electrode, as well as high volume flowrate for aspiration. In particular, in this mode of ablation outputenergy delivery during treatment is adjusted for increased tissueremoval with continuous aspiration flow volume to pull tissue closer tothe wand for more efficient ablation rates. The high volume flow ratewill result in having lower electrode circuit impedance, and regular(but uncontrolled) plasma collapse. Thus, plasma collapse is expected inthe high mode based on the aggressive aspiration flow, but the high modemay implement a minimum volume flow rate, and thus a minimum peristalticpump speed, even if such minimum speed results in plasma collapse. Theplasma should be reinstated as tissue contact ensues.

In the high mode of operation, the processor 500, executing a program,controls the voltage generator 516 and peristaltic pump 118 to implementlow target impedance for the electrode circuit. In some embodiments, thecontroller 104 may provide predetermined output energy, and forimpedance values falling within a predetermined range, the controller104 may control impedance based on changes in speed of the peristalticpump 118. For variations in impedance that fall outside with apredetermined range, the control strategy may also rely on changes inoutput energy supplied by the voltage generator 516. For example,control action in response to decreasing impedance (as calculated basedon the current and/or voltage applied to the active electrode) mayinvolve slowing the peristaltic pump 118, but only to predeterminedminimum volume flow rate.

The illustrative vacuum mode of ablation is designed specifically forquickly removing loose tissue and tissue fragments within the surgicalfield. For this reason, the illustrative vacuum mode is characterized byvariable output energy provided to the active electrode, as well as thehighest volume flow rate as between the various modes (when theaspiration is active). In particular, in this mode of ablation outputenergy delivery during treatment is desired to be optimized for fastdigestion of debris within the surgical field in conjunction with a highvolume flow rate in order to attract debris to the wand tip. The highvolume flow rate will result in lower electrode circuit impedance. Whentissue debris is in contact with the electrode, the flow is lessened tobetter digest the tissue. When the electrode has no tissue in itsproximity, the voltage is dropped to lessen electrode wear.

FIG. 6 shows a graph that relates possible energy ranges (output RFenergy) to aspiration flow rate (shown as pump speed settings) for fourexample modes of ablation—low mode, medium mode, high mode, and vacuummode. In particular, for each mode of ablation the electrosurgicalcontroller 104 is programmed to operate within an energy range of outputRF energy and a range of aspiration flow rates. For example, in the “lowmode” of ablation described above controller 104 may be pre-programmedto operate within an energy range from 25-50 Watts, and aspiration flowrange from an example “−1” (i.e., reverse motor direction) to “5”, whichin some cases may result in an aspiration flow in a range from 0-45ml/min. For the example “medium mode” of ablation, described above,controller 104 may be pre-programmed to operate within an energy rangefrom 50-150 Watts, and aspiration flow range from an example “0” (i.e.,peristaltic motor stopped) to “5”. For the example “high mode” ofablation described above, controller 104 may be pre-programmed tooperate within an energy range from 150-400 Watts, and aspiration flowrange from an example “1” to “5”. For the example “vacuum mode” ofablation described above, controller 104 may be pre-programmed tooperate within an energy range from 350-400 Watts, and aspiration flowrange from an example “2” to “5”. These example output energy and flowrates and energy ranges are merely examples, and could vary in actualvalues.

Moreover, FIG. 6 illustrates that, within at least some of the modes ofablation, differing energy setpoints are contemplated. That is, in someexample systems, within the pre-programmed energy ranges, the processor500 (executing a program) implements at least three, and in some casesfive, energy setpoint levels within a mode of ablation to enable changesof both the output RF energy (and correspondingly the flow rate in thevicinity of an active electrode). For example, FIG. 6 illustrates thateach of the low mode, medium mode, and high mode may have an initial ordefault energy setpoint and a corresponding default aspiration volumeflow setpoint (labeled in each mode with a “D” and triangular symbol).In FIG. 6, the default energy setpoints are shown to reside in themiddle of the energy range, but in other cases the default energysetpoints may be at the lower or upper ends of the respective energyranges.

Considering the low mode as representative of modes of ablation havingmultiple energy setpoints within the energy range, two energy setpointswith energies above the default energy setpoint may be implemented, andthese higher energy setpoints are designated in FIG. 6 as the (+) and(++) energy setpoints. By way of manually activating a control input(e.g., foot pedal, button on the controller, graphical user interfacesuch as a touch screen, or a button on the wand), the surgeon mayincrease the setpoint energy level to the plus (+) or (++) levelperformance. Likewise, two energy setpoints with energies below thedefault energy setpoint may be implemented, and these lower energysetpoints are designed in FIG. 6 as the (−) and (−−) energy setpoints.By way of manually activating a control input (e.g., foot pedal, buttonon the controller, or a button on the wand), the surgeon may decreasethe setpoint energy level to the minus (−) or (−−) level performance.Any number of energy setpoints within a mode of ablation may beimplemented. While the low mode and medium mode in FIG. 6 each have fiveenergy setpoints, the high mode is illustrative shown to have only threeenergy setpoints within the energy range—a default energy setpoint, aplus (+) level and a minus (−) level. It is likewise possible for thevacuum mode to have varying energy setpoints, but no such energysetpoints are illustrated in FIG. 6 to exemplify that in some systemsnot all modes have multiple energy setpoints within their respectiveenergy ranges.

By way of example, in the previously described “high mode” the default(D) energy setpoint may be about 250 Watts, and an aspiration flowsetpoint of level 3 (which, for example, may result in an aspirationflow rate of 200 ml/min). By advancing the controller 104 operationalparameter to the plus (+) setpoint due to either a desired increase inoutput energy or aspiration flow rate, the controller 104 then increaseseach performance characteristic in a complementary fashion, such as byadjusting the output energy to about 325 Watts and the aspiration flowsetpoint to level 4 (which, for example, may result in an aspirationflow rate of 300 ml/min). Alternatively, a user may desire a decrease inboth output energy and flow rate setpoint, and may accordingly choose toset back the energy setpoint to the minus (−) level performance and flowrate setpoint. Thus, each mode of operation may have a plurality ofperformance levels delineated by energy setpoints and flow setpoints,yet operation of any of the plurality of performance levels shall stillbe considered to be within a particular mode of ablation.

The specification now turns to implementation of the control loopswithin controller 104. In accordance with example systems, the controlloops are implemented as software by the processor 500, but in otherembodiments portions or all the control loops may be implemented indiscrete logic. FIG. 7 shows, in block diagram form, the logicalinteraction of the control loops, as well as interaction betweensoftware executed by the processor and various components of thecontroller 104. In particular, FIG. 7 shows software as the variouscomponents within the software block 700, and likewise shows the voltagegenerator 516, the motor speed control 536, the active terminal 518, andcurrent sense transformer 532. Other components of the controller 104are omitted so as not to unduly complicate the figure. Moreover, FIG. 7also illustrates a plasma 702 in operational relationship to aspirationflow through an aperture (shown by arrow 704 in relation to tube 706).

In accordance with example systems, the software 700 generates orselects an energy value (shown as E in the figure) as well as a flowsetpoint (shown as Fsp in the figure). The energy value E and flowsetpoint Fsp are generated or selected based the mode of ablation chosenby the surgeon (and the energy setpoints within the mode of ablation).The example energy value E may be applied to the voltage generator 516in any suitable manner, such as those discussed above. In examplesystems, the energy value E is a single value representing the desiredoutput energy, but in other cases the energy value E may be a valueindicative of voltage to be created by the voltage generator 516, or acombination of values representing a desired voltage or electricalcurrent to be created by the voltage generator 516. Based on the energysetpoint Esp, the voltage generator 516 may produce the desired voltageon the active terminal 518, ultimately creating plasma 702. Duringperiods of time when voltage is being supplied by the voltage generator516, the electrical current may be measured by the current transformer532, and an indication of the instantaneous electrical current may besupplied to the software 700 as indicated in the FIG. 7.

In accordance with example systems, during the low mode, medium mode,high mode, and certain periods of time in the vacuum mode, the software700 implements closed-loop control. More particularly, the examplesystem may apply the flow setpoint Fsp to aproportional-integral-differential (PID) control loop 708. In examplesystems, the flow setpoint Fsp is a single value representing thedesired volume flow of fluid, but in other cases (and for ease in codingthe control loops) the flow setpoint Fsp may be a value indicative ofelectrical current since electrical current provided by the voltagegenerator and volume flow of fluid are directly proportional duringperiods of time when plasma is present. In the example logicalcontrol-loop flow, the flow setpoint Fsp may be applied to summationblock 710. The summation block 710 may create an error signal 712 bysubtracting the feedback parameter (in this illustrative case, theelectrical current measured by the current transformer 532, FIG. 5) fromthe flow setpoint Fsp. As illustrated, the feedback parameter may besubjected to various filtering operations in filter block 714, and suchfiltering is discussed in greater detail below. The error signal 712 maybe applied to a proportional block 716, an integral block 718, and adifferential block 720. Each block may be associated with gain value:G_(P) for the proportional block 716; G_(I) for the integral block 718;and G_(D) for the differential block 720. Each example block 716, 718,and 720 produces a response signal, and the respective response signalsare summed at summation block 722. The summed signal is then convertedto a proper format for the motor speed controller 536 and applied to themotor speed controller 536 to control peristaltic pump 118 speed. Notall the PID blocks 716, 718, and 720 need be implemented simultaneously.In some cases only proportional-integral (PI) control may suffice, andthus the differential block 720 may be omitted or disabled (e.g., bysetting the gain G_(D) to zero).

The specification now turns to an explanation of PID control loop 708control in the low mode, medium mode, high mode, and certain periods oftime during the vacuum mode. First, consider that the controller 107,plasma 702, and volume flow of fluid 704 have reached a steady statepoint that matches the various setpoints, and that the RF voltagegenerator 516 is cable of providing a substantially constant voltageregardless of impedance. Then considerer that, perhaps based on movementof the active electrode of the wand against tissue, the electrodecircuit impedance increases. Increasing impedance results in decreasingelectrical current flow. Responsive to the decreasing electrical currentflow the summation block 710 creates an increasing magnitude errorsignal 712 that is applied to various blocks 716, 718, and 720. The endresult of this example situation is an increasing flow of fluid drawninto the aperture (by increasing the peristaltic pump speed) responsiveto the electrosurgical controller detecting the active electrode is inoperational relationship with tissue.

Now consider again that the controller 107, plasma 702, and volume flowof fluid 704 have reached a steady state point that matches the varioussetpoints, and that the RF voltage generator 516 is capable of providinga substantially constant voltage regardless of impedance. Thenconsiderer that, perhaps based on of movement of the active electrode ofthe wand away from tissue, the electrode circuit impedance decreases.Decreasing impedance results in increasing electrical current flow.Responsive to the increasing electrical current flow the summation block710 creates a decreasing magnitude error signal 712 that is applied tovarious blocks 716, 718, and 720. The end result of this examplesituation is a decreasing flow of fluid drawn into the aperture (bydecreasing the peristaltic pump speed) responsive to the electrosurgicalcontroller detecting the active electrode has moved away from tissue.The specification now turns to distinguishing the various modes ofablation.

The various modes of ablation are distinguishable based not only on theoutput energy and flow ranges discussed above (and specific setpointswithin the respective ranges), but also based on the gain setpointsimplemented. For example, the low mode of ablation may implement a firstset of gain values G_(PL), G_(IL), and G_(SL), and the high mode ofablation may implement a second set of gain values G_(PH), G_(IH), andG_(DH) that are distinct from the low mode of ablation. Moreover, insystems that implement different output energy and flow setpoints withina mode of ablation, each energy setpoint may have a set of gain values.For example, the low mode of ablation may implement a first set of gainvalues at the default energy setpoint G_(PLD), G_(ILD), and G_(DLD), andthe low mode of ablation may implement a second set of gain values atthe (+) energy setpoint G_(PL+), G_(IL+), and G_(DL+), and so forth.

Moreover, other parameters may be associated with the PID control loop708 that are not specifically delineated in FIG. 7. For example, theintegral block 718 may have additional parameters in the form of resettime for the integration, or maximum allowed values of the integralblock 718 response. Such additional parameters may reduce or prevent“wind up” of the response of the integral block 718 in certainsituations (such as extended periods of plasma collapse or significantvoltage generator pulsing). Further still, the range of motor speedcontrol is different between the example modes of ablation, with somemodes (e.g., the low mode) having the ability to stop and even reversedirection of the peristaltic pump, and with other modes implementingminimum non-zero speeds for the peristaltic pump (e.g., the high mode),and thus the summation block 722 may have additional parameter whichlimit the range of values that can be applied to the motor speedcontroller 536 regardless of the actual summation of the various inputs.

In some example systems, gain scheduling may be implemented by the PIDcontrol loop 708 (FIG. 7). That is, in some systems within a particularmode of ablation different gains may be used as a function of themagnitude of the error signal 712. Consider as an example of gainscheduling the proportional block 716. In systems where gain schedulingbased on the magnitude of the error signal 712 is used, when themagnitude of the error signal 712 exceeds a first predeterminedthreshold, a first gain value G_(P1) may be used by the proportionalblock 716, and when the magnitude of the error signal 712 exceeds asecond higher predetermined threshold, a second gain value G_(P2) may beused by the proportional block 716 where the second gain value isdifferent than the first gain value. Each example block 716, 718, and720 may use gain scheduling within a particular mode of ablation, anddifferent gain schedules may be used based on the setpoints within eachmode of ablation (i.e., a first gain schedule for the default mode, anddifferent gain schedule for each of the (+), (++), (−), and (−−)setpoints. Moreover, gain scheduling may be used within some or all ofthe modes of ablation. For example, the gain value for the proportionalblock 716 for the low mode of ablation G_(m) may be a set of values,such that G_(PL)={G_(PL1), G_(PL2), G_(PL3)}. As another example, thegain value for the proportional block 716 for the high mode of ablationG_(PH) may be a set of values, such that G_(PH)={G_(PH1), G_(PH2),G_(PH3)}. Further still, as the electrode wears due to use (discussedmore below), the gains setpoints, and gain schedules, may be changed.

In some example systems, the controller 104 is pre-programmed with allthe various parameters used to identify and implement the modes ofablation. For example, the ROM 504 of the controller 104 may bepre-programmed with the some or all of the various parameters used toidentify and implement the modes of ablation, and the software 700 (alsostored on the ROM 504) may, when executed, read the parameters andimplement the modes of ablation based on the parameters. In othersystems, however, the various parameters used to identify and implementthe modes of ablation may be dependent on the wand 102 (e.g., theexposed surface area of the electrode 202). Thus, the values associatedwith each mode of ablation may be wand 102 dependent, and again thecontroller 104 may be pre-programed with some or all the variousparameters for each wand 102 which may be used with the controller 104.In such systems, the wand 102 may be identified by the controller by anysuitable means (e.g., identified by the surgeon selecting the wand froma list of supported wands using the display 130 and buttons 132, or thewand may be identified electrically by the controller based oninformation readable by the pins in the connector 114). In yet stillfurther cases, different sets of parameters may be used with the samewand to implement different characteristics of the modes of ablation.

Still referring to FIG. 7, the discussion now turns to example filteringperformed in the filtering block 714. In particular, while a valueindicative of the electrical current read by the current transformer 532may be logically applied directly to the summation block 710, in someexample systems the overall control of the plasma 702 may be bettercontrolled by implementing filtering within the filtering block 714. Inorder to logically tie the example filtering scenarios to the plasmacontrol, a brief description of operational phenomenon associated withthe voltage generator 516 and plasma 702 is in order. The firstoperational phenomenon is plasma 702 “collapse” (i.e., the plasma isextinguished). Plasma collapse is more likely in some operationalsituations, such as in the modes of ablation implementing higher volumeflow of fluid. During periods of time when the plasma has collapsed,electrical current may flow through fluids and/or tissue abutting theelectrode 202 of the wand in a thermal mode, and in the impedance toelectrical current flow in the thermal mode is lower than the impedanceof plasma. In most cases, the plasma is quickly re-established. Thus,plasma collapse may result in a high frequency electrical current“spike”. The second operational phenomenon is voltage generator 516“pulsing”. Pulsing of the voltage generator 516 is a temporary cessationof voltage and current flow to the electrode 202 based on the outputenergy delivery meeting or exceeding a predetermined output energythreshold. For example, in some systems the voltage generator 516 maytemporarily cease providing a voltage (and therefore cease providing acurrent) when the output energy delivery meets or exceeds 400 Joules persecond. When output energy delivery is stopped, the plasma isextinguished, electrical current drops (e.g., to zero). When outputenergy is again provided the system progresses through a thermal mode(in which a current spike is seen) and then to a plasma mode.

Volume flow of fluid provided during periods of plasma collapse andgenerator pulsing has little effect on re-establishing the plasma, andthus in some example systems no (or very little) control action inregard to the volume flow of fluid may be taken responsive to the plasmacollapse and generator pulsing events. Thus, in accordance with examplesystems the filtering block 714 implements control strategies to dealwith plasma collapse and generator pulsing. FIG. 8 shows, in blockdiagram form, one example control strategy logically implemented withthe filtering block 714. In particular, the feedback parameter in theform of an indication of electrical current being supplied by thegenerator is applied to an averaging block 800. As the name implies, theaveraging block 800 creates a running average value of the indication ofelectrical current during periods of time when plasma is present (e.g.,over the last 500 milli-seconds, or the last second). The runningaverage value, as well as the indication of electrical current beingsupplied, is applied to a multiplexer 802. During periods of time ofgenerator pulsing, the multiplexer 802 passes the running average valueto downstream logical components. That is, PID control loop 708 isprovided the running average value created by the averaging block 800,rather than the instantaneous indication of electrical current beingsupplied, during periods of generator pulsing. In this way, the PIDcontrol loop 708 may take little or no action responsive to thegenerator pulsing. When the generator pulsing event is completed, andplasma is re-established, the multiplexer 802 again provides theinstantaneous indication of electrical current being supplied to thedownstream logical components. Thus, the averaging block 800 andmultiplexer 802 may be considered to address pulsing issues; however,other logical mechanism may be equivalently used.

The indication of electrical current flow propagating from themultiplexer 802 may then be applied to a low-pass filter block 804. Asthe name implies, the low-pass-filter block 804 filters the signal toremove high frequency components, such as current spikes associated withplasma collapse. Thus, PID control loop 708 is provided a low-passfiltered version of the indication of electrical current created by thelow-pass filter block 804. In this way, the PID control loop 708 maytake little or no action responsive to plasma collapse. Thus, thelow-pass filter block 804 may be considered to address the plasmacollapse issue; however, other logical mechanism may be equivalentlyused.

The specification now turns to control in the vacuum mode of ablation inaccordance with example systems. In the vacuum mode of ablation, duringperiods of time when the active electrode 202 is not in operationalrelationship with tissue (as determined based on low overall impedance),a relatively high volume flow of fluid is drawn into the aperture.However, when the active electrode encounters tissue (as determinedbased on increasing impedance), rather than increase the volume flow offluid, in the vacuum mode the opposite control strategy is implemented.That is, when the active electrode encounters tissue (and the impedanceincreases), the volume flow of fluid drawn into the aperture decreases.The theoretical basis for the control strategy is that the vacuum modeis designed for quickly removing free floating and/or loosely heldtissue, but where the volume density of the tissue is low. Thus, theremay be large volumes of bodily fluids or saline containing no tissuedrawn into the aperture. The volume flow of fluid is high during periodsof time when no tissue is present near the active electrode, but thevolume flow of fluid slows during periods of time when tissue is inoperational relationship with the active electrode to enable increaseddigestion rate of tissue and more thorough molecular dissociation andreduction of the tissue to decrease clogging. In some cases, duringperiods of time when tissue is in operational relationship with theactive electrode, the volume flow of fluid may be controlled in afashion similar to the other modes of ablation. In yet still othercases, the lack of tissue may be sensed by pulsing of the generator.

Returning briefly to FIG. 7, in some example systems the volume flow offluid during the vacuum mode is based on the PID control loop 708standing alone, in combination with a change in flow setpoint Fsp. Thatis, during periods of time when no tissue is in operational relationshipwith the active electrode, the flow setpoint Fsp in the vacuum mode maybe set very high; however, when tissue is in operational relationshipwith the active electrode, the flow setpoint Fsp is reduced to implementthe decrease in the volume flow of fluid. Moreover, the various gainsassociated with the blocks 716, 718, and 720 may be changedsimultaneously with changing the flow setpoint Fsp responsive to thecontroller detecting the active electrode is in operational relationshipwith the tissue. However, other control strategies are possible, such asdiscussed with respect to FIG. 9.

FIG. 9 shows, in block diagram form, a logical interaction of thecontrol strategies in the vacuum mode, as well as interaction betweensoftware executed by the processor and various components of thecontroller 104. In particular, FIG. 9 shows software as the variouscomponents within the software block 700, and likewise shows the voltagegenerator 516, the motor speed control 536, the active terminal 518, andcurrent sense transformer 532. Other components of the controller 104are omitted so as not to unduly complicate the figure. During periods oftime when plasma is being maintained by an active electrode of a wand inthe vacuum mode, but where no tissue is in operational relationship tothe active electrode, the flow setpoint Fspv may be directly applied tothe motor speed controller 536 though logical multiplexer 900. As shown,the speed is set, in many cases predetermined, and no changes are madethe based on any feedback parameter. Thus, during the period of timewhen no tissue is in operational relationship with the active electrode,the example system implements open-loop flow control. However, when thesystem determines that there is tissue in operational relationship tothe active electrode. The multiplexer 900 may be operated to couple thecontrol signal derived from the PID control loop 708 to the motor speedcontroller 536. Given that the flow setpoint Fspv is higher than theflow setpoint Fsp in this situation, the flow of fluid into the aperturedecreases, and then closed-loop flow control is exercised responsive tothe electrosurgical controller detecting the active electrode is inoperational relationship with tissue.

Simultaneously with implementing the various control strategies for themodes of ablation, the controller 104 may also perform clog detection.That is, in some situations a large piece of tissue may enter theaperture 404 behind the active electrode 400 causing a clog either atthe location of the aperture, or at another location within the wandand/or tubing. A clog reduces or stops the volume flow of fluids intothe aperture. In accordance with the various embodiments, the presenceof a clog may be detected by the processor 500 (executing a program)indirectly based on other parameters. For example, when a clog ispresent the impedance of the electrode circuit changes and thuselectrical current flow changes and becomes stable (in relation to thenon-clog condition). Moreover, when a clog is present the fluids withinthe flexible tubular member 116 may pool and/or become stationary andthus cause localized temperature increases. Further still, peristalticpump 118 speed is related to impedance changes (assuming correspondingflow of fluid), but in the presence of a clog changes in peristalticpump speed have little or no effect on impedance. The stator movementcan be sensed, for example, by Hall Effect Sensors. These sensors showthat the stator up and down movement is a predictable cycle in normaloperation. When there is a clog, the cycle of movement is dampened andthe clog may be detected.

Thus, in accordance with the example embodiment the controller 104 (moreparticularly the processor 500 executing a program) determines thepresence of a clog based on two or more of the above-noted parameters.For example, the processor 500 may make an initial determination of aclog based on an impedance change and then stabilization, and the clogdetermination may be verified by implementing control changes in volumeflow of fluid that have no effect on impedance. As yet another example,the processor 500 may make an initial determination of a clog based onan impedance change and then stabilization, and the clog determinationmay be verified by reading increasing temperature of the fluid flow inthe tubular member 116 (such are read by temperature measurement device304 of FIG. 3). Other variations are possible. For example, the initialdetermination may be based on reading increasing temperature, and theverification based on either impedance changes and/or lack of controleffect. Additionally, pressure variations or oscillations of the fluidwithin tubular member 116 may be sensed in the form of tubing wallpulsing, causing the flexible tubular member 116 to variably expand andcontract. Inasmuch as impedance and electrical current are related (fora constant or known applied voltage), changes in impedance and changesin electrical current may be interchangeable in the determinationsand/or verifications. Any suitable measure of change of impedance (orelectrical current) may be used, such as variations, changes in standarddeviation. The specification now turns to electrode wear considerations.

The active electrode of the example wand 102 is the location about whichplasma is formed. The plasma not only ablates various tissues, but theplasma also etches the active electrode, thus removing metallic materialover time. Etching of the active electrode reduces the size and/orexposed surface area of the active electrode, and also reduces the“sharpness” of asperities (if present) defined by the active electrode.After continued use, the active electrode may be reduced in size to thepoint that the therapeutic benefit is reduced or eliminated—that is,used beyond useful life. If used beyond the useful life, the activeelectrode may fail, such as by cracking, splitting, or even becomingdetached from the distal tip 108, thus lodging itself inside the body atthe treatment site. Failure of the active electrode may result inserious complications, and thus should be avoided.

The amount of plasma time to which an active electrode may be exposedbefore failure varies based on the mode of ablation and the specifics ofthe wand 102. Modes of ablation using higher energies result in moreaggressive etching of the active electrode, while modes of ablationusing lower energies result in less aggressive etching. For example, theinventors of the current specification estimate that the example wand102 discussed with respect to FIGS. 2-4 may have a useful life of 8minutes if used exclusively in the high mode of ablation and have auseful life as long as 30 minutes is used exclusively in the low mode ofablation. It is contemplated that a surgeon will vary the modes duringany particular electrosurgical procedures, and thus the useful life willbe dependent upon the amount of time spent in each mode of ablation. Inthe example, the useful life may fall somewhere between 8 and 30minutes.

In order to gauge the state of the active electrode, in accordance withexample embodiments the electrosurgical controller 104 is designed andconstructed to measure an indication of active electrode wear. In oneexample embodiment, the measurement is made just prior to each plasmaactivation. In particular, in one embodiment the controller 104 (andmore particularly, software executed by the processor 500), receiving acommand to create the plasma but prior to commanding providing outputenergy sufficient to create a plasma, commands the voltage generator toapply a test voltage to the wand circuit (e.g., terminal 518, conductorsin the multiconductor cable 112, the active electrode 400, the returnelectrode, conductive fluids and other fluids/tissue between the activeelectrode and the return electrode, etc.). The test voltage is lowenough that plasma is not created, but high enough to induce anelectrical current flow through the wand circuit. The controller 104measures the electrical current flow (e.g., by way of currenttransformer 532), and based on the voltage and current calculates animpedance of the wand circuit. The impedance of the fixed components,such as terminals, wiring, and even the conductive fluids, is known orcalculable in advance. However, a portion of the overall impedanceassociated with the active electrode is dependent upon the remainingsize of the active electrode and/or the remaining exposed surface area.Thus, the impedance of the active electrode can be measured. Once theactive electrode impedance has been measured (and assuming the impedancevalue is above a predetermined threshold), the controller 104 maycommand the voltage generator 516 to increase the voltage to create theplasma. On the other hand, if the active electrode impedance indicatesthe active electrode is beyond its useful life, the controller 104 mayrefrain from providing sufficient voltage to create the plasma, andprovide an alarm or alert (e.g., posting a message on display device130).

In one example system, during periods of time when the impedance of theelectrode circuit is being measured, the controller may apply a voltagein the range of 5-20 Volts. In some cases, the voltage is an alternatingcurrent (AC) voltage, and thus the 5-20 Volts may be a peak or RMSvalue. In other cases, the voltage applied may be a direct current (DC)voltage, in which case the indication of active electrode wear includesonly a purely resistive component. In one example situation, a wand 102having an active electrode that has not previously been exposed toplasma may have a real component of the measured impedance in the rangeof 40-100 Ohms. After the active electrode has been used to the point ofbeing beyond useful life, the same active electrode may have a real partof the impedance of 200 Ohms or above.

In accordance with yet still further embodiments, the controller 104 mayalso calculate or estimate the remaining useful life of the activeelectrode. In particular, during of time when the voltage generator isproviding output energy sufficient to establish plasma proximate to theactive electrode, the controller 104 may calculate or estimate theremaining useful life of the active electrode based on the current modeof ablation (e.g., based on the current energy level being provided).The controller may provide an indication of the remaining useful life tothe surgeon, such as by displaying the estimated remaining useful lifeon the display device 130 of the controller 104. If the surgeon switchesto a different mode of ablation, or a different energy setpoint within amode of ablation, the calculated or estimated remaining useful lifevalue will likewise change. That is, the value indicative of remaininguseful life may be estimated or calculated assuming that the controller104 remains operating in the current mode of ablation (and energysetpoint level) for the remaining useful life, but as the surgeonchanges modes of ablation and/or energy setpoint level within the modeof ablation, the value indicative of remaining useful life will likewisechange.

In yet still further embodiments, the value indicative of useful lifemay be checked, verified, or adjusted based on measured impedance. Thatis, the controller 104 may calculate or estimate remaining useful lifeduring periods of time when plasma is present. When the impedance of theelectrode circuit is measured (e.g., response to a command to createplasma, or perhaps automatically after cessation of plasma), theremaining useful life may be updated to reflect electrode wear. That,is, the calculate or estimated value indicative of remaining useful lifemay be increased if the measured impedance of the electrode circuit(when no plasma is present) indicates less wear than expected. Likewise,the calculate or estimated value indicative of remaining useful life maybe decreased if the measured impedance of the electrode circuit (when noplasma is present) indicates more wear than expected. Moreover, thecontroller 104 may update the rates at which the value indicative ofuseful life is decremented during times when plasma is present based onactual rates calculated using two or more impedance measurements.

FIG. 10 shows a method in accordance with some embodiments, portions orall of which may be implemented by a program executed on a processor. Inparticular, the method starts (block 1000) and proceeds to maintainingplasma proximate to an active electrode of an electrosurgical wand, theplasma created based on the delivery of output energy to the activeelectrode by an electrosurgical controller, the output energy within apredetermined first energy range (block 1002). During periods of timewhen output energy is being delivered within the first energy range, themethod may comprise: providing output energy at a first default energysetpoint by the electrosurgical controller, the first default energysetpoint within the first energy range (block 1004); and providingoutput energy at a second energy setpoint by the electrosurgicalcontroller, the second energy setpoint different than the first defaultenergy setpoint, the second energy setpoint within the first energyrange, and implementing the second energy setpoint responsive to theelectrosurgical controller receiving a command (block 1006). Thereafter,the method ends (block 1008), possibly to be immediately restarted witha second energy range.

FIG. 11 shows a method in accordance with some embodiments, portions orall of which may be implemented by a program executed on a processor. Inparticular, the method starts (block 1100) and proceeds to maintainingplasma proximate to an active electrode of an electrosurgical wand, theplasma created based on the delivery of output energy to the activeelectrode by an electrosurgical controller, the output energy within apredetermined first energy range (block 1102). During periods of timewhen output energy is being delivered within the first energy range, themethod may comprise: controlling flow of fluid drawn into an aperture ofthe electrosurgical wand at a first flow rate (block 1104); andincreasing flow of fluid drawn into the aperture responsive to theelectrosurgical controller detecting the active electrode is inoperational relationship with tissue (block 1106). Moreover, the methodmay comprise maintaining plasma proximate to the active electrode, theplasma created based on the delivery of output energy to the activeelectrode within a predetermined second energy range, the second energyrange distinct from the first energy range (block 1108). During periodsof time output energy is being delivered within the second energy rangethe method may comprise: controlling flow of fluid drawn into theaperture at a second flow rate (block 1110); and decreasing flow offluid drawn into the aperture responsive to the electrosurgicalcontroller detecting the active electrode is in operational relationshipwith tissue (block 1112). Thereafter, the method ends (block 1114),possibly to be immediately restarted.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications are possible. It is intended that the following claims beinterpreted to embrace all such variations and modifications.

While preferred embodiments of this disclosure have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the scope or teaching herein. The embodimentsdescribed herein are exemplary only and are not limiting. Because manyvarying and different embodiments may be made within the scope of thepresent inventive concept, including equivalent structures, materials,or methods hereafter thought of, and because many modifications may bemade in the embodiments herein detailed in accordance with thedescriptive requirements of the law, it is to be understood that thedetails herein are to be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. An electrosurgical method comprising: maintainingplasma proximate to an active electrode of an electrosurgical wand, theplasma created based on delivery of output energy to the activeelectrode by an electrosurgical controller, the output energy within apredetermined first energy range, and during periods of time when outputenergy is being delivered within the first energy range; controlling anaspirating flow of fluid drawn into an aperture of the electrosurgicalwand at a first flow rate; and increasing the aspirating flow of fluiddrawn into the aperture responsive to the electrosurgical controllerdetecting the active electrode is in operational relationship withtissue; and maintaining plasma proximate to the active electrode, theplasma created based on delivery of output energy to the activeelectrode within a predetermined second energy range, the second energyrange distinct from the first energy range, and during periods of timeoutput energy is being delivered within the second energy range;controlling the aspirating flow of fluid drawn into the aperture at asecond flow rate; and decreasing the aspirating flow of fluid drawn intothe aperture responsive to the electrosurgical controller detecting theactive electrode is in operational relationship with tissue.
 2. Theelectrosurgical method of claim 1 wherein decreasing flow of fluid drawninto the aperture further comprises decreasing a flow setpointresponsive to the electrosurgical controller detecting the activeelectrode is in operational relationship with tissue.
 3. Theelectrosurgical method of claim 1: wherein controlling flow of fluiddrawn into the aperture at the second flow rate further comprisesimplementing open-loop flow control; and wherein decreasing flow offluid drawn into the aperture further comprises implementing closed-loopflow control responsive to the electrosurgical controller detecting theactive electrode is in operational relationship with tissue.
 4. Theelectrosurgical method of claim 1 wherein maintaining plasma associatedwith the first energy range further comprises: providing output energyat a default energy setpoint by the electrosurgical controller, thedefault energy setpoint within the first energy range; and thenproviding output energy at a second energy setpoint by theelectrosurgical controller, the second energy setpoint different thanthe default energy setpoint, the second energy setpoint within the firstenergy range, and implementing the second energy setpoint responsive tothe electrosurgical controller receiving a command.
 5. Theelectrosurgical method of claim 4 wherein the second energy setpoint isat least one selected from the group consisting of: a higher outputenergy than the default energy setpoint; and a lower output energy thanthe default energy setpoint.
 6. The electrosurgical method of claim 4wherein the controller receives the command by way of at least oneselected from the group consisting of: actuation of a foot pedal;actuation of a button on the electrosurgical wand; actuation of a buttonon the electrosurgical controller; and manipulation of a graphical userinterface on the electrosurgical controller.
 7. The electrosurgicalmethod of claim 4 further comprising, after providing output energy atthe default energy setpoint and providing output energy at the secondenergy setpoint, providing output energy at a third energy setpoint bythe electrosurgical controller, the third energy setpoint different thanthe default energy setpoint and the second energy setpoint, the thirdenergy setpoint within the first energy range, and implementing thethird energy setpoint responsive to the electrosurgical controllerreceiving a command.
 8. The electrosurgical method of claim 1 whereinmaintaining plasma associated with the first energy range furthercomprises: providing output energy at a default energy setpoint by theelectrosurgical controller and controlling aspiration of fluid at afirst flow setpoint; and then providing output energy at a second energysetpoint and controlling aspiration at a second flow setpoint, thesecond energy setpoint being within first energy range and beingdifferent than the default energy setpoint, the second flow setpointdifferent than the first flow setpoint, and implementing the secondenergy setpoint responsive to the electrosurgical controller receiving acommand.
 9. The electrosurgical method of claim 1 further comprisingdelaying the delivery of output energy to the active electrode until atleast the first flow rate of flow of fluid drawn into an aperture of theelectrosurgical wand is established.
 10. The electrosurgical method ofclaim 1 further comprising, prior to at least one step of maintainingplasma, measuring impedance of an electrode circuit that comprises theactive electrode.
 11. The method of claim 1, wherein during periods oftime when output energy is being delivered, adjusting the output energyso as to maintain plasma proximate the active electrode.
 12. Theelectrosurgical method of claim 1 further comprising detecting a clogcondition that alters the flow of fluid through the aperture based on anincrease of temperature of tubing associated with the aperture.
 13. Theelectrosurgical method of claim 12, wherein the temperature is sensed bya temperature measurement device abutting an outer surface of thetubing.
 14. An electrosurgical method comprising: maintaining plasmaproximate to an active electrode of an electrosurgical wand, the plasmacreated based on delivery of output energy to the active electrode by anelectrosurgical controller, the output energy within a predeterminedfirst energy range, and during periods of time when output energy isbeing delivered within the first energy range; measuring at least oneelectrical parameter presented by of an electrode circuit impedancecomprising the plasma and active electrode; controlling an aspiratingflow of fluid drawn into an aperture of the electrosurgical wand at afirst flow rate; and increasing the aspirating flow of fluid drawn intothe aperture in response to an increase in the electrode circuitimpedance; and maintaining plasma proximate to the active electrode, theplasma created based on delivery of output energy to the activeelectrode within a predetermined second energy range, the second energyrange distinct from the first energy range, and during periods of timeoutput energy is being delivered within the second energy range;measuring the at least one electrical parameter indicative of anelectrode circuit impedance comprising the plasma and active electrode;controlling the aspirating flow of fluid drawn into the aperture at asecond flow rate; and decreasing the aspirating flow of fluid drawn intothe aperture responsive to an increase in electrode circuit impedance.